A small study suggests that women 70 and older who have existing heart problems or diabetes are more likely to develop heart problems if treated with Herceptin (chemical name: trastuzumab) for breast cancer.

The research was published online on Aug. 9, 2011 in the Annals of Oncology.

Herceptin is used to treat HER2-positive breast cancers. HER2-positive breast cancers make too much of the HER2 protein. The HER2 protein sits on the surface of cancer cells and receives signals that tell the cancer to grow and spread. About one out of every four breast cancers is HER2-positive. HER2-positive breast cancers tend to be more aggressive and harder to treat than HER2-negative breast cancers.

Herceptin is a targeted therapy medicine that works by attaching to the HER2 protein and blocking it from receiving growth signals. Herceptin, which is given intravenously, is approved by the U.S. Food and Drug Administration to:

treat advanced-stage, HER2-positive breast cancers

lower the risk of recurrence (the cancer coming back) of early-stage, HER2-positive breast cancers with a high risk of recurrence

Women treated with Herceptin may have side effects, including:

high blood pressure

joint and back pain

hot flashes

headache

diarrhea

Heart muscle damage and heart failure are serious but uncommon side effects of Herceptin. Most previous studies looking at the safety and risks of Herceptin focused on younger women. This study looked at heart side effects caused by Herceptin in older women.

The researchers looked at the medical records of 45 older women diagnosed with either early-stage or advanced-stage HER2-positive breast cancer. The women had an average age of 76 -- 11 were older than 80.

56% of the women got Herceptin before and/or after surgery for early-stage breast cancer.

44% of the women got Herceptin to treat advanced-stage breast cancer.

The women treated for advanced-stage cancer had metastatic breast cancer, which means the breast cancer had spread to another part of the body away from the breast, such as the liver, brain, or bones.

The researchers looked at results from heart function testing (called left ventricular ejection fraction or LVEF) that was done when Herceptin treatment started and again an average of 4.5 months later.

Twelve women (more than 25%) had severe heart function problems while getting Herceptin. Four of these women had symptoms of the heart issues, while the other eight had no symptoms.

The researchers found that Herceptin was more likely to cause heart problems in:

women being treated for metastatic breast cancer

women who already had one or more heart disease risk factors (high blood pressure, for example) before getting Herceptin

women who already had heart disease before getting Herceptin

diabetic women

Heart damage related to Herceptin treatment can happen at any time during treatment. Still, heart function can recover when Herceptin treatment stops.

About 70% of all breast cancers are diagnosed in women older than 65. This study suggests that the risk of Herceptin-related heart damage is higher than doctors thought for older women.

If Herceptin is or will be part of your breast cancer treatment plan, ask your doctor about this study, especially if you're older than 65. It's a good idea to ask your doctor about your risk of Herceptin-related heart damage and how your heart function will be evaluated before and during Herceptin treatment.

In the Breastcancer.org Herceptin pages, you can learn more about how Herceptin works, when it's used, and what to expect during treatment.